Apparatus for heat-trimming foam material

Abstract

A thermoplastic material, such as a sheet of polystyrene or polyethylene foam, is placed between a trim guide, which may be a die mold or press, and is in the form of at least two heat-conducting metal pieces, one of which is movable towards the other. The trim guide is pressure-operated to pressurize the material along the area to be trimmed. This may be an edge of a plastic sheet, the perimeter of an article produced from the material, or may be holes or slots to be cut in the material. A knife or other tool, heated to a temperature high enough to melt the material, is then moved along the trim guide. The knife vaporizes the pressurized material along the trim guide, which creates a definitive point at which melting or vaporization of the material stops. The trim guide is made from metal having high heat-conductivity, such as aluminum which has sufficient heat-conductivity to create a point at which melting, caused by the knife vaporizing the material, stops.

I claim as my invention: 
     
       1. An apparatus for heat-trimming thermoplastic foam materials by melting the portion of the thermoplastic foam to be trimmed comprising, two opposed non-heated, heat conducting metallic die parts made from a metal of high heat-conductivity and forming a trim guide for the foam material, and limiting the trimming action by absorbing the heat of melting of the foam material along the aligned edges of said die parts, as trimmed, and means carrying said absorbed heat away from said die parts,   pressure means moving at least one die part relative to the other to open said die parts and receive the foam material to be trimmed therebetween, and operable to exert sufficient pressure on the foam material to compress the foam material along the edge to be trimmed,   a source of heat at a temperature at least high enough to melt or vaporize at least a portion of the exposed foam material, and trim the exposed material along the die parts by melting at least a portion of the material up to the edges of the die parts,   means applying the source of heat along the exposed edge of the foam material to melt or vaporize the edge of the foam material along the two die parts, said die parts having sufficient heat-conductivity to stop melting of the exposed material by absorbing the heat of melting of the foam material as pressurizing the foam material and provide a clean edge of the trimmed material without flash.   
     
     
       2. The apparatus of claim 1 in which the source of heat is a knive heated to the melting or vaporizing temperature of the foam material, and the die parts compressing the foam material are made from aluminum. 
     
     
       3. The apparatus of claim 2 in which coolant passageways are provided in the metallic die parts to accommodate the circulation of coolant therealong and retain the temperature of the die parts to a temperature sufficient to stop melting of the projecting edge of the foam material at the die parts, and to thereby create a region at which melting of the foam material by the source of heat stops. 
     
     
       4. The apparatus of claim 1 in which the opposed die parts of metal of high heat-conductivity include one recessed die part and another mating die part having a bottom surface conforming to and spaced from the recess of the recessed die part to accommodate the placing of a piece of foam material therebetween, wherein a stripper extends about the mating die part for stripping the trimmed and formed piece of foam material from the recessed die part, wherein the stripper has a heat-conducting pressure member extending thereabout and cooperating with the stripper and recessed die part, to compress the edge of the foam material to be trimmed, and wherein the source of heat is movable along the die parts to trim the foam material along the edge of the recessed die part by melting or vaporizing the foam material. 
     
     
       5. The apparatus of claim 4, in which the source of heat is a heated knife extending about one die part and moved toward and from said pressure member to effect trimming of the exposed edge of the piece of foam material by melting or vaporizing the exposed edge of the foam material to the outer surfaces of the die parts, which die parts stop melting of the foam material by the heat-conductivity thereof. 
     
     
       6. The apparatus of claim 5, in which the piece of foam material is placed between the die parts in a sheet-like form as it comes from the oven and is at oven temperature, and wherein the heated knife has spaced slots therein to leave tabs between the formed piece and sheet of foam material to adhere the formed piece to the sheet of foam material as removed from between the die parts. 
     
     
       7. The apparatus of claim 6, in which the die parts are made from aluminum and have passageways for liquid coolant therein, wherein coolant is circulated through the passageways and the stripper is spring-biased to strip the formed article from the one die part upon separation of said one die part from said other die part.